1. Based on the Person class in the Lecture Notes, define a subclass Teacher including one instance variable, office ( String type), and two methods, setOffice , and toString that returns the name,...

1. Based on the
Person
class in the Lecture Notes, define a subclass
Teacher
including one instance variable,
office
(String
type), and two methods,
setOffice, and
toString
that returns the name, and office. Then write a driver that prompts the user to input a teacher's name and office information from the keyboard, and then output the teacher’ info to the monitor by invoking the
toString
method.

2. Based on the
Time
class and its derived class
ExtTime
class in the Lecture Notes, write a driver to test the polymorphism. That is, given the two objects of
Time
and
ExtTime
classes as below,

ExtTime x =
new
ExtTime();
Time y =
new
Time();
read the values of
x
and
y
from the keyboard, and then increase both objects by
two seconds
by invoking the
increment() method twice (also inherited to the subclass). Then pass the two objects through the same
display
method so to output the info of objects to monitor. Use a loop, so the process could run continuously.
Requirements: the time values should be read in the format of
hh:mm:ss.

3. Based on the
Line
class in the Lecture Notes, read the four data (x₀, y₀, x₁, y₁) for a
Line
object from the keyboard, and output its length to the monitor by calling the corresponding method. Use a loop, so the process could be run continuously.

Page 1 of 18 Module 6 Object-Oriented Programming Contents Module 6 Object-Oriented Programming.....................................................................................1 OOP Inheritance ......................................................................................................................2 Using the toString Method .......................................................................................................5 Section Exercises .....................................................................................................................8 More Examples: Point and Pixel Classes ............................................................................... 10 OOP Composition ................................................................................................................. 11 Section Exercises ................................................................................................................... 13 Polymorphism ....................................................................................................................... 15 Chapter Exercises .................................................................................................................. 17 Page 2 of 18 Java is one of the most popular Object-Oriented Programming (OOP) languages. The traditional (C, Pascal, Fortran) program is a function-based or structured program that consists of some functions: fun1 ( …) .. fun2 ( …) .. An object-oriented program (OOP) consists of objects: obj1 … obj2 … OOP Inheritance With a base class or super class, we can define its derived class or subclass that includes inherited methods and new methods. A super-class is declared as: public class Time { private int hrs; private int mins; private int secs; public Time() // default constructor { hrs = 0; Page 3 of 18 mins = 0; secs = 0; } public Time(int h, int m, int s) { hrs = h; mins = m; secs = s; } public void set(int h, int m, int s) { hrs = h; mins = m; secs = s; } public void writeOut() { if (hrs < 10)="" system.out.print("0");="" system.out.print(hrs="" +="" ":");="" if="" (mins="">< 10)="" system.out.print("0");="" system.out.print(mins="" +="" ":");="" if="" (="" secs="">< 10="" )="" system.out.print("0");="" system.out.print(secs);="" }="" public="" void="" increment="" ()="" {="" secs="" ++;="" if="" (secs=""> 59) { secs = 0; mins ++; if (mins > 59) { mins = 0; hrs ++; if (hrs > 23) hrs = 0; } } } public boolean equal (Time other) { return (hrs==other.hrs && mins==other.mins && secs==other.secs); } } A derived class or subclass named ExtTime includes the string zone. Then we can declare a subclass ExtTime derived from its super class Time shown as below. ALL of the variables and methods of the super class are inherited into its derived classes or called subclasses, but the methods of the subclass with the same name will overwrite that of the super class (also called the base class). The diagrams of the above classes are illustrated as below. Page 4 of 18 public class ExtTime extends Time { private String zone; public ExtTime () { super(); // invoking the default constructor of Time class zone = “EST”; } public ExtTime ( int h, int m, int s, String z) { super(h, m, s); // invoking the general constructor of Time zone = z; } public void set (int h, int m, int s, String z) { set(h, m, s); // invoking the set inherited from Time class zone = z; } // … set(int h, int m, int s); // inherited from Time class // … increment (); // inherited from Time class public void writeOut () // overwrite that of Time class { super.writeOut(); System.out.print(" " + zone); } public boolean equal (ExtTime other) // overwrite that of Time { return (super.equal(other) && zone==other.zone); } } Page 5 of 18 Note: The set method inherited from the Time class is different from the other set method since they have different parameters. The writeOut and equal methods of the ExtTime class will overwrite that of the Time class. In the constructors of the ExtTime class, the variables (hrs, mins, and secs) of the Time class can be initialized through the keyword, super, meaning its super class, Time class. Since the variables are declared as private in the Time class, they could NOT be directly accessed by any members of the ExtTime class. Example (a) Write the code to declare an object x of ExtTime initialized with 8:35:0 PST. ExtTime x = new ExtTime(8, 35, 0, “PST”); (c) Write the code to declare an object y of ExtTime initialized with 0:0:0 EST. ExtTime y = new ExtTime(); Using the toString Method The toString method is briefly introduced in the last module for Fraction Class. In Java, the toString method is defined in the base class. That is, it could be used in any of user-defined classes. It is very convenient to use since it can be omitted when it is passed as an argument in the standard output statement, System.out.println. An example is as follows.